Three-phase slurry reactors are well known to those skilled in the art. Typical examples of chemical processes that are carried out in three-phase slurry reactors are those which make use of solid catalyst particles, use at least one gaseous reactant, and produce a product that is liquid under reaction conditions. Many of such tri-phasic reactions are highly exothermic. Examples of such processes include hydrogenation processes, hydroformylation, alkanol synthesis, the preparation of aromatic urethanes using carbon monoxide, Kolbel-Engelhardt synthesis, polyolefin synthesis, and Fischer-Tropsch synthesis.
Fischer-Tropsch synthesis is a technology for preparing hydrocarbons from mixtures of gases based on hydrogen and carbon monoxide, conventionally known as synthesis gas. A summary of some of the work on the Fischer-Tropsch synthesis reactions is contained in the Bureau of Mines Bulletin, 544 (1955) entitled “Bibliography of the Fischer-Tropsch Synthesis and Related Processes” H. C. Anderson, J. L. Wiley and A. Newell. In general, the Fischer-Tropsch technology is based on the use of a reactor for chemical reactions that are carried out in triphasic systems where the gas phase reactants bubble into a slurry of catalyst solids in liquid. The gas phase consists of synthesis gas, a mixture of hydrogen and carbon monoxide with a molar ratio H2/CO varying from at least about 0.5 to about 3. The dispersing liquid phase within the reactor comprises reaction products and serves as a heat transfer medium. The solid phase is represented by catalyst solids that may be present in a variety of forms.
The Fischer-Tropsch reaction product that is discharged from the reactor consists of a slurry that must be processed to separate the solid catalyst from the liquid phase reaction products. In addition, in order to maintain the reactor slurry at a constant level and to maintain a desired volume of activated catalyst within the reactor, a portion of the slurry can be continuously or intermittently removed from the reactor for separating the catalyst from the liquid reaction products and recycling the separated catalyst to the reactor. However, there are difficulties that are typically encountered in separating catalyst particles from liquid hydrocarbons products. The present invention relates to the separation of catalyst solids from the slurry of hydrocarbons produced by Fischer-Tropsch synthesis. Several methods have been described for separating catalyst particles from Fischer-Tropsch wax. A report on the subject is entitled “Status Review of Fischer-Tropsch Slurry Reactor/Catalyst Wax Separation Techniques” that was prepared for the U.S. Department of Energy, Pittsburgh Energy Technology center by P. Z. Zhou, Burns and Roe Services Corporation, February, 1991. This report described filters, magnetic separators and settling devices, most of which were not successful or were not deemed commercially viable.